Bench Grinders & Lathe Tools.

[Pete W.]

I referred in a previous thread to the subject of HSS lathe tools.  That thread was intended to be humorous but I also indicated that I had some questions about the grinding of HSS lathe tools that I would raise in a separate thread - well, here it is.

First of all, a bit of background.  I've always kept my grinding machine in a separate building away from my lathe & drill-press.  This involves running out an extension power lead and also temporarily moving some other 'stuff' out of that shed to make room to access the grinder.  I'm enthusiastic but I don't achieve as many workshop hours per year as most of you guys!  The net result of this is that, despite running my lathe since about 1970, I've done very little grinding of HSS tool blanks.  I've managed quite well with a selection of Cintride brazed carbide tools of various shapes.  These only require an occasional quick kiss with a carborundum slip stone or a DMT diamond hone.

Now, in this post, I'd like to get Modders' opinions and comments on a couple of grinding machine and grindstone topics.  Please note that I am concerned with the common double-ended bench grinder, not the more exotic 'tool & cutter grinders'.

The first topic is bizarre.  I recently visited the local branch of a national chain of tool merchants.  I have been dissatisfied for some time with my tool grinding facilities so I asked the staff member what sort of range of grinding wheels they kept in stock.  He replied that they kept none in-branch 'because they have a 12 month shelf-life' so I would have to order from their Head Office via their web-site.  To say that his reply surprised me would be a huge understatement!  To explore its implications, it's reasonable to assume that a grinding wheel in use on a machine can't have a 'shelf life' longer than if it were on the shelf but I know of bench grinders whose wheels haven't been changed in decades!  How about that?

My second topic concerns the presentation of tool blanks to the grinding wheel.  The conventional wisdom is that the tool blank should only be presented to the rim of the wheel, never to its flat sides.  I recently bought a second double-ended bench grinding machine and its User Instructions echo this restriction.  However, in grinding a lathe tool, the major part of the job is to form a prism shape with plane faces, not concave faces.  Furthermore, Harold Hill's book on tool sharpening has illustrations clearly showing tools being presented to the side of the wheel.  I look forward to your comments. 

[DMIOM]

Pete,

I can't offer any definitive advice, but I have previously found the UK HSE's "Safety in the use of Abrasive Wheels" useful, you can buy the hardcopy, but it is also available as a free PDF download. I'd suggest you might have a look yourself; on a quick read the only pertinent reference I can spot is "....All organic bonded wheels for hand-held applications will bear a use-by date of three years from the date of manufacture....."

Dave

[PekkaNF]

Yesh...organically bonded wheels have expiry date and that is pretty common on cut out wheels, they don't mature that well

http://www.highspeedtraining.co.uk/hub/grinding-wheel-marking-system/

The expiry date if it’s an organic bonded wheel (this will be 3 years from the date of manufacture).

This marking is often on steel cap/hub, often sample discs that come with grinder are allready expired.

Short dig from the garage revealed this:

Pekka

[gerritv]

If I recall correctly, Harold shows the tool being presented to the corner of the wheel, not the full side?

The exception is drill grinding where there is very little pressure.
The only sure way to get a flat side is to use a cup type wheel, where you are grinding on the side :-)

Gerrit

[chipenter]

Using the side of the can generate heat , and iff used for long periods may crack the wheel , but only iff hard pressure is used and the tool is red hot .

[AdeV]

I bought a cup-type wheel to go on one side of my bench grinder (had to turn up a bush to make it fit properly - gotta love lathes!). Now I just need a few Round Tuits to make a suitable tool rest so I can grind true flat HSS tools... but since I mostly use carbide insert tooling (the Glanze range from Chronos mostly, being fairly good value, or whatever I can find second hand on the 'bay), any surviving Tuits have been deployed elsewhere...

[fatal-exception]

I use the side of the wheel all the time and have been doing so for 30 years and have never had any problems. Maybe they don't want you using the side because the tool rest usually dosen't wrap around the wheel? I say use any part of the wheel required to get the result you need. 

Paul

[Pete.]

The single best piece of advice I can give you is get hold of a good dressing tool. I can't stand to grind on my bench grinder now until I give the wheel a quick swipe to open it up. It really makes a world of difference not only in terms of grinding speed but also in heat input. A dull wheel grinds slowly and heats up the part quickly.

[vtsteam]

I think side pressure on the wheel is probably considered bad because you're putting the wheel sideways in tension, which isn't the forte of most forms of ceramics. Also the possibility of wearing a groove and making a stress riser there. That plus vibration. Well and getting something caught between table and the stone, and really jamming that side pressure on.

Having just proposed that theory, I use the side of the wheel all the time, and use wheels 10 years old. I also grind lathe tools on the front of the wheel often, and live with the hollow grind that results. In other words I do everything totally wrong.

In defense of such foolishness, I start the grinder and stand away for a half minute, and just keep the above worries in mind, dress (not seriously grind) only small (1/4") HSS lathe tools on the side of the wheel (mainly for top rake), use light pressure, avoid making grooves, etc. In other words I use what I think is common sense -- others may disagree -- and they might even be right!

I don't try to shorten big bolts on the side of the wheel, nor axeheads, nor staging nails. Or even initially shape a lathe tool there. A manufacturer sells grinders to all kinds of people, who do all kinds of things to them, so if I were a manufacturer, I would not only tell the public not to grind on the side of the wheel, but not to grind on the front, either.  Rather just put it in the shop to admire.

[sparky961]

Make up some better tool rests. The flimsy sheet metal ones that come with most consumer bench grinders are just about useless. I use the flimsy ones still but if I spent a lot of time at the grinder I'd make some very rigid adjustable ones.

[Pete W.]

Hi there, again, all,

First of all, I apologise for starting a thread and then doing a disappearing act!  Things cropped up!!

Pete,

I can't offer any definitive advice, but I have previously found the UK HSE's "Safety in the use of Abrasive Wheels" useful, you can buy the hardcopy, but it is also available as a free PDF download. I'd suggest you might have a look yourself; on a quick read the only pertinent reference I can spot is "....All organic bonded wheels for hand-held applications will bear a use-by date of three years from the date of manufacture....."

Dave

 

I confess that I hadn't been thinking of organic bonded wheels - in my experience, double-ended bench grinders have always been fitted with vitreous bonded wheels.

Am I right in thinking that organic bonded wheels are used when it's necessary to profile the wheel to grind some complex shape?

On an earlier thread, long, long ago, I got a hot (near incandescent) response when I broached the subject of 'to use or not to use' non-new wheels.  Soon after I started this thread, Keith Rucker posted a video on his YouTube channel showing a table well covered with second-hand wheels that he had acquired as a job-lot.  He said that he was going to keep some of the wheels for his own use but invited offers from viewers who might take the others off his hands (for a fair price).  On page 5.17 of The Model Engineer's Handbook (third edition), Tubal Cain (i.e. the Brit, alias Tom Walshaw) writes 'the only safe speed for second-hand wheels of unknown provenance is zero.'  I find that hard because I have, among my stash, a medium & fine pair of virgin vitreous bond wheels, a white saucer wheel and a white cylindrical cup wheel, any or all of which would enhance my tool-grinding capabilities.  The provenance of the medium & fine pair is not unknown, I bought them several years ago, I've looked after them carefully, they are still in their original packing and they 'ring' healthily.  The provenance of the two white wheels is more obscure - the saucer wheel also 'rings' healthily but the shape of the cylindrical cup wheel doesn't lend itself to the 'ring' test.  Application of the 'precautionary principle' here might decouple authors (and forum posters) from litigation but it also promises to condemn a lot of potentially usable wheels to scrap (that can't be an environmental plus!!).  I'll just add that, while going through my stash, I did find a nice new old stock fine green-grit wheel that failed the 'ring' test - closer examination revealed a Y-shaped crack and it fell into three pieces while being handled!  I did scrap that one while weeping a little.

In addition to my original 7" Black & Decker double-ended grinder, I have a smaller single ended grinder.  This has the wheel and rest on the left-hand end and is fitted to accept a flexible shaft on its right-hand end.  I wondered about fitting the white cylindrical cup wheel to that machine but it would be turning the wheel the wrong way.

I recently made an impulse buy, a modern 150 mm double ended machine.  It's rated at 370 Watts but with a 10 minutes ON, 15 minutes OFF duty cycle.  The motor runs quietly enough but when I saw how the wheels turned, the expression that came to mind was 'swash plate'!!  I've left it too long to ask the seller to accept a return and, besides, the purchase price was alleged to be reduced.  In his book, Harold Hall describes mounting an entire double ended grinder on the bed of his lathe and using cross-slide and top-slide to true the grinder shaft ends while it revolved under its own power - I'll probably be trying that some time.  The wheel mounting washers are pressings but look to be true enough.

Well, this has been a long post, and no photos!!! 

[Pete.]

It's the pressed steel side plates that cause the wobble. I turned some heavy duty ones for my grinder and the wheels run lovely and true. You only need do the back plate.

[PekkaNF]

Safety is importat. I believe that information that answers on question "why not this way, and why this way" produces safer work habits than blaket "Don't do it" without any explanation.

If we just take the view that when something is dangerous, we better just stop convesation there is very little left in out hobby.

If I recall correctly, Harold shows the tool being presented to the corner of the wheel, not the full side?

The exception is drill grinding where there is very little pressure.
The only sure way to get a flat side is to use a cup type wheel, where you are grinding on the side :-)

Gerrit

I second this one. I have used the double ended bench grinder that way and it saves whole lot of wheel. Prolonged use side of the wheel not only thins and weakens the wheel, but also makes rings, grooves, and stops on the side and it is not really good idea to true the sides of the wheel.

The idea of using corner is to feed blank from front and not to press on the side, this produces same effect (effect on the tool blank) that feedin the blank sideways BUT without excessive wear to side of the wheel.

I went a little furher and feed the blank at acute angle into rim of the wheel. You end up with somewhat rhombic wheel, but it is better than using pure side presure.

Downside is that the corner wears off, but good news is that you are not using pure side of the wheel. You eventually need to true the face to prevet the rim disapearing completely and to remove steps, but it did work pretty well to me. This way you completely avoid leaving a stop/step onto side of the wheel. The rim wears faster, but this is the direction the wheel is intended to work and you can true the rim of the wheel.

Pekka

[vtsteam]

Grinding on the side of the wheel in my experience does not put grooves in the side of the wheel for the same reasons that grinding on the front of the wheel, in my experience, doesn't put grooves there, either. Reason: I move the part around to even out wear so it doesn't put grooves in the wheel.

Plus I use the side for light dressing of small pieces, not full out grinding to reduce mass, as I mentioned earlier.. And yep, I do mainly use the side of the wheel at the corner. Makes sense from a practical grinding point of view anyway since the surface speed is greatest there.

Why try to grind a groove in the side of the wheel, and locate that where the wheel is ineffective? To solve that possibiltity by a total noob, naturally a manufacturer needs a blanket statement: don't use the side of the wheel.

Incidentally, putting a deep groove in the front of a wheel isn't a lot "safer" than the side. The thin remaining groove walls can break off -- and if you think about it -- you ground on their sides in making it, didn't you?

In short, don't make grooves at all.

[PekkaNF]

Good point of avoiding any delicate steps or portrusions on normal bench grinding wheels.

While I completely agree with you, you must admit that many "cllasic" parting out and boring bar designs lead themselves careless side grinding stockremoval process if you don't put though to it or don't have much experience - yet. Those shouders can easily produce grooving.

Often use of the side can be eliminated with alternative approach:
http://www.sherline.com/pages/images/grndfig9.gif

So...if someone would ask an advice, I would tell that generally it is better to avoid using the sides for any but the lightest finnish and see alternative methods like using the cup wheel or different approach, like this:
http://www.tascione.com/Sherlinelathe_ins/grinding.htm

Pekka

[AdeV]

I bought a cup wheel for my bench grinder. It came from a 2nd hand tool shop, so is of unknown provenance, but it's now spent several hours spinning on my grinder with no ill effects. The advantage of the cup, of course, being you can grind flat surfaces... I did have to make a bushing to fit my grinder, but hey - that's why we have lathes isn't it...?

What I really need to do now is make an adjustable tool rest to suit the cup wheel... another on on the Round Tuit waiting list...

[chipenter]

I madesometing similar to  Harrold Halls grinding rest improovers repeatability no end .http://www.homews.co.uk/page145.html

[Fergus OMore]

hat I really need to do now is make an adjustable tool rest to suit the cup wheel... another on on the Round Tuit waiting list...

I'm getting into one of those Eccentric Acute grinder things- or is it two? Bought the bits at Doncaster Show for one.

Lashed out at Axminster and bought a double ended grinder with a 80 grit wheel on one end and a paving stone grit on the other but I want my CBN to go somewhere.

So a hint for those who have problems finding angles and all this tilting stuff. Work on the flat- ie with chipboard or whatever and  get the angle with the maths in inches

Dia of wheel x diameter of stone x 0.00088" and crunch the result  to the nearest 1/16th and arrange packing up or down on centre of spindle.

Hope this helps!

Norm

[Pete W.]

SNIP

I recently made an impulse buy, a modern 150 mm double ended machine.  It's rated at 370 Watts but with a 10 minutes ON, 15 minutes OFF duty cycle.  The motor runs quietly enough but when I saw how the wheels turned, the expression that came to mind was 'swash plate'!!  I've left it too long to ask the seller to accept a return and, besides, the purchase price was alleged to be reduced.  In his book, Harold Hall describes mounting an entire double ended grinder on the bed of his lathe and using cross-slide and top-slide to true the grinder shaft ends while it revolved under its own power - I'll probably be trying that some time.  The wheel mounting washers are pressings but look to be true enough.
 

I eventually got this grinder to the top of the 'to-do' list.  The photos show the complete machine, then various stages of dis-assembly of the RH wheel & guard and finally the dial gauge readings.

The shaft extending from the ball-race has three sections, diameters 14.5 mm, 12.72 mm and thread M12.  I measured the peak-to-peak run-out of the two plain sections at between 0.007" and 0.010" (sorry about the mixed units).  There's a centre drilling in that end of the shaft and, presumably, one in the LH end also, so I assume that the motor rotor and shaft are turned between centres.  I reckon you'd have to do something fairly clever or astonishingly stupid to get 7 to 10 thou run-out that close to the bearing journal and centre!

The shaft surface finish was interesting, not so much a cylinder as a very fine thread, about 75  to 100 tpi!  I re-assembled the machine before I up-loaded the photos and the photos don't show the surface finish.  If I dismantle it again, I'll take another photo just showing the shaft extension and its finish.

I couldn't measure any run-out in the face of the step between the two shaft sections - the step is too small to give my DTI a satisfactory contact.

The abrasive wheel from that end of the machine lies flat on the surface of my dining table so I think that's not the cause of the swashing motion.  I'd like to measure the lateral run-out at the outer edge of the wheel (when mounted) but I didn't want to apply my DTI stem to the wheel.  If I think of a safe way to take that measurement, I'll post again.

Right, photos:

[Fergus OMore]

Years ago, I had the same sort of trouble which was traced to rotten wheels, out of balance and worse.

From what I have read, it is 'normal' to replace the wheels with something more in keeping with our hobby demands

HTH

Norm

[Pete W.]

As promised, I've taken a close-up photo of the shaft of the grinding machine, see below.

If this is the current professional standard for surface finish, does this mean that my efforts to emulate the surface finish achieved by the YouTube machinists community have been a misguided waste of time?

                   

[Fergus OMore]

Read John Ruskin on 'Price'.  Not much of a model engineer but they did name a Cambridge University after him.

[mattinker]

Looks like a suitable case for turn undersize and sleeve!

Regards, Matthew

[Pete.]

That's normal for a cheap grinder. The plates rely on that little step but it's inadequate. This is why I turned my own side plates. I actually turned the plates as a 'plate and hub' so that the bit that sits on the shaft is longer. I then use wheels which have a larger hole, and it works very well, they run nice and true.

[Pete W.]

Coincidentally, I was called in by Simon (a neighbour) whose polishing machine had blown up!!          

It's an elderly Wolf double-ended grinder fitted with two shaft extensions to take the polishing mops. 
He'd been busy polishing when there was a loud bang, a bright flash and all the lights went out!!!          

We took the base-plate off the machine and found that the contents of the capacitor had exited the can in a spectacular manner.  Sorry, no photo!  Fortunately, the inscription on the outside of the capacitor can was complete and readable.  I did a bit of resistance checking and found a 9.5 Ω run winding but, at first, couldn't find any conductivity through the start winding.  Oh, I thought, either the start winding has blown or the centrifugal switch is defective.  We'll have to take the bell off.  That was as much as we achieved at the first session - other pressing matters shut that session down.

Two evenings later, off came the RH shaft extension and the bell to reveal NO centrifugal switch and nice honey-coloured windings showing no signs of over-heating.  Just to check we took off the other bell, complete with rotor, and found NO centrifugal switch that end either.  Things were looking up!!  This time, I must have been less fumble-fingered with the Fluke probes because I found approx 20 Ω between the wires to the start winding.  I also 'meggered' both windings to frame and got an infinity reading.  A replacement capacitor is on order.

The reason I've recounted all this simple stuff is that I am inspired to hope that my own grinder (depicted in my earlier photos) is also a capacitor start & run type.  I'll have to listen carefully for a 'click' during its start-up and run-down.  If it, like Simon's, has no centrifugal switch, the complete removal of the rotor will be that much simpler and I'd be able to mount the whole rotor in my lathe to re-machine and sleeve the shaft extensions.  The squirrel cage rotor will clear the bed and I'd support the outer bearing in the fixed steady.

Harold Hall's method of mounting the entire grinder on the lathe bed and turning its shafts using its own power is do-able but means inverting the tool when machining one end because the rotor is turning clockwise.

Has anyone else trod this path before me?

Watch this space!